考虑侧阻增强效应的基桩极限承载力解析算法

摘要

常规基桩竖向极限承载力计算方法难以考虑由于端阻力提高而引起的侧阻增强效应。分析基桩侧阻增强效应的形成机理，在此基础上，采用 Meyerhof 对数螺旋线破坏模式模拟桩端土体破坏状态，并引进极限上限理论分析桩端与桩侧土体在极限承载情况下的能量传递规律，利用虚功原理导出桩侧土体对桩身增加的法向压力值，由此根据摩尔库伦理论提出了考虑侧阻增强效应的基桩竖向极限承载力公式。与现场基桩承载力试验数据的对比表明，桩基规范常规算法明显低估了基桩的极限承载力，而本文推算的理论公式则更接近于实测静载荷试验值，表明考虑侧阻增强效应后可更合理评估基桩承载能力。对影响基桩侧阻增强效应的各主要因素进行了探讨，分析结果表明，随桩端土体强度或桩径的增加，侧阻增强效应作用愈明显，该结论对基桩工程设计具有一定的借鉴意义。%Shaft resistance enhancement effect of pile due to the increasing of tip resistance is hard to be consid-ered in conventional method of vertical bearing capacity.Firstly,the mechanism of shaft resistance enhancement effect is analyzed deeply in the paper.On this basis,logarithmic spiral line of Meyerhof is adopted to simulate the failure modes of soil below pile tips,and upper -bound method of limit analysis is introduced to analyze the energy transfer laws of soil below and around piles.Therefore,the incremental normal stress along pile is de-duced with the principle of virtual work.The ultimate axial bearing capacity of pile is also obtained by taking the shaft resistance enhancement effect into consideration via Mohr -Coulomb theory.Comparison of calculated val-ues to field data shows that the present method was more reasonable in predicting bearing capacity of pile,and the conventional method underestimates the bearing capacity of pile.Finally,several key parameters relating to shaft resistance enhancement effect are analyzed,and the result shows that shaft resistance enhancement effect would be even more obvious with the increase of soil strength under pile tip and pile diameter.This conclusion could provide a reference to engineering practice.